CHICKEN bindings to stb_image_write

Requirements

None, stb_image_write.h v1.09 is embedded in the egg.

API

[procedure] (write-png pixels width height components #!key flip compression stride filter)
[procedure] (write-jpg pixels width height components #!key flip quality)
[procedure] (write-tga pixels width height components #!key flip rle)
[procedure] (write-bmp pixels width height components #!key flip)

Writes the u8vector pixels to (current-output-port) using the image format of the procedure name. The pixel format depends on components, which represents the number of bytes per pixel:

1: y8 (gray)
2: ya16 (gray + alpha)
3: rgb24
4: rgba32

Extra parameters are:

• flip specifies whether to flip the image vertically before outputting
• png compression sets the zlib compression quality. defaults to 8, try higher values for more compression
• png stride is the distance in bytes from the first byte of a row of pixels to the first byte of the next row of pixels.
• png filter forces a particular filter type for all scanlines. defaults to trying all and picking the most efficient (#f), other valid values are 0-4.
• jpg quality specifies lossy compression amount as a percentage (defaults to 80)
• tga rle enables or disable run-length-encoding compression. it is on by default, set to #f to disable rle compression

Note that on 32-bit systems, blobs cannot be larger than 16M. This also limits image sizes as pixel data is stored in a blob.

Example

(use stb-image-write)

(define %pixels
  (let ((r '(255   0   0 255))
        (b '(  0   0 255 128))
        (_ '(  0   0   0   0)))
    (list->u8vector
     (flatten
      (list b b b b b b b b b b b b b b b b
            b _ _ _ _ _ _ _ _ _ _ _ _ _ _ b
            b _ _ r r r _ r r r _ r r _ _ b
            b _ _ r _ r _ r _ _ _ r _ r _ b
            b _ _ r r r _ r r r _ r _ r _ b
            b _ _ r r _ _ r _ _ _ r _ r _ b
            b _ _ r _ r _ r r r _ r r _ _ b
            b _ _ _ _ _ _ _ _ _ _ _ _ _ _ b
            b b b b b b b b b b b b b b b b)))))

(with-output-to-file "red.png"
  (lambda ()
    (write-png %pixels 16 9 4)))

TODO

• test png stride
• see if it's possible to write data to port without copying memory

Source

The source is located here.